Accepted 5th May, 2014
The study investigated the constraints in benthic macro invertebrate productivity in semi arid river with human interferences. The effects of benthic macro invertebrates predation and impaired water were studied in a 500m mesh net 1 m3 exclosures situated in the upstream and downstream of a river. The common species of benthic predators include birds, fish, crab and odonata. The control was a cageless open control area, where all predators could feed. The highest mean number of taxa was found in the control exclosure of unpolluted control sites. Number of taxa in exclosures where large fish were absent were two-fold higher than where all predators were present at test sites. The mean density of the benthic macro invertebrate taxa caught in all the sites was not significantly different (t test, p>0.05, df=8) between the control and test sites. The results do not constitute proof of a detrimental impact of pollution. The idea of population regulation in the Runde River is complex; a wet summer may drown them, a hot dry summer may dessicate them, emigration and immigration may exacerbate population changes and predation may be an important force structuring populations.
Keywords: benthic macro invertebrates, predation, impaired water, semi-arid river